Device for measuring force variations, mechanical deformations, hydrostatic pressures and temperature, and associated measurement method

Abstract

The invention relates to a non-intrusive measurement method and device intended to measure a variation in longitudinal force, other than exerted by a hydrostatic pressure, and / or a hydrostatic pressure variation, relating to a host structure of interest, including: - a sensor (3) comprising at least one optical waveguide (7) which is installed on one of the surfaces or in the wall of a cylindrical test body (9) and deforms in its elastic domain, each optical waveguide locally describing a circular helix and carrying at least one transducer (11) which is sensitive to orientation and configured to perform a selective measurement of a first primary variable and of a second primary variable; - a computer (17) configured to selectively calculate the local variation of a longitudinal force δF, other than exerted by a hydrostatic pressure, applied to the test body and / or the local variation in hydrostatic pressure ΔP applied to the test body (9) according to the true relative variations of the measurements of the first and / or second primary variables.

Description

[0001] DESCRIPTION

[0002] Title: Device for measuring variations in force, mechanical deformations, hydrostatic pressures and temperature, and associated measuring method

[0003] TECHNICAL FIELD

[0004] The present invention relates to a non-intrusive device intended to selectively measure a variation in force, other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure, as well as a variation in temperature, and an associated measuring method. The invention applies to the field of instrumentation, and more precisely to the measurement of force, mechanical deformations, hydrostatic pressures and temperature, on the surface or within a deformable mechanical structure.

[0005] STATE OF THE PRIOR ART

[0006] There is, particularly in environments subject to significant constraints, such as certain structures, in particular tanks or pressurized pipes, a need to carry out measurements of mechanical deformations, hydrostatic pressures and / or temperatures, particularly for monitoring purposes, to ensure their structural mechanical integrity during their operation, but also for the purpose of predictive maintenance.

[0007] Measurements within structures themselves using in situ sensors are particularly difficult to carry out when temperatures, mechanical deformations, or even hydrostatic pressure are likely to vary simultaneously, due to the cross-sensitivity in temperature, mechanical deformation and hydrostatic pressure of the transducers generally used.

[0008] This problem is all the more delicate because these quantities can vary significantly. For example, the temperature can vary by several tens of degrees Celsius in the most common applications, and in extreme conditions, by several hundred degrees Celsius.

[0009] For example, the temperature of gaseous molecular hydrogen H2 can reach 70°C at 700 bar during the filling process of a tank, with a hydrostatic pressure difference of several hundred bar between its internal and external walls, and mechanical deformations of up to 0.6% (6000 pm / m) at 700 bar in the case of a type IV tank with a carbon-epoxy resin matrix. However, the effect of temperature on the measurement provided by a sensor is generally sufficient in itself to bias any measurement of mechanical deformation that may result if it is not perfectly compensated, in addition to the fact that hydrostatic pressure can also interfere.

[0010] For example, a thermal compensation error of around 0.038°C is sufficient in itself to lead to a measurement error of 1 bar in pressure for a metal pipe with an external diameter of 102.3 mm and a wall thickness of 13.49 mm according to a standardized standard.

[0011] In addition to the lack of thermal compensation, there are mechanical forces; thus, a variation of 600 N in a force applied longitudinally to this same pipe is responsible for a measurement error of 1 bar in its internal hydrostatic pressure, or a measurement error of the order of 0.72 μm / m in its longitudinal mechanical deformation.

[0012] It is therefore advantageous for a sensor whose transducers (housed within or on the surface of a deformable structure) are sensitive to the effects of temperature, hydrostatic pressure and longitudinal mechanical deformation applied to them, to be able to separate each of these three effects, in order to provide, independently of each other, the measurement of the variations of each of these three effects acting on the instrumented structure, compared to an arbitrary reference state.

[0013] Currently, there is a measurement technique based on the use of an ellipsoidal, preferably spherical, test body made of elastic, homogeneous material with known mechanical properties, intended to be included in a host structure, using a strain measuring fiber, mechanically secured to this test body, so as to transmit to it the strains of the host structure (document WO 2014 / 140496). The three-dimensional measurement of the strains of the host structure is then based on the Eshelby inclusion problem, in order to determine the strain field of the host structure as it would exist in the absence of the inclusion of this test body within this host structure.Apart from the fact that this sensor does not compensate for the thermal effects acting on each of the transducers (in this case Bragg gratings), the inclusion of a foreign body of several tens of millimetres in diameter within a host structure remains problematic, as it very often causes local weakening, which can ultimately lead to the ruin of the structure.

[0014] Document FR 3 117 582 B1 is an improvement of the solution proposed in document WO 2014 / 140496 so as to reduce its intrusive effect, with a tangential rather than a through arrangement of the transducers in relation to the spheroidal-shaped inclusion: the problem of compensating for thermal effects on each of the transducers, making it possible to provide a measurement of a purely mechanical nature in a variable temperature field, is however still not resolved by this approach.

[0015] Furthermore, there are also measurement techniques based on the use of an optical fiber with birefringence created by the residual mechanical deformations of the structure, within which the sensor is integrated.

[0016] Such a technique is described for example in document US 5 591965. This technique is based on the use of a birefringent optical fiber with several Bragg gratings photo-inscribed at distinct Bragg wavelengths. These Bragg gratings are positioned at the same location in the optical fiber, therefore subjected to the same temperature, which makes it possible to recompose the components of the local tensor of mechanical deformations independently of the effects of temperature, since it involves the two-by-two differences of the raw measurements made by each transducer.

[0017] According to this state-of-the-art technique, variations in hydrostatic pressure and longitudinal forces interact. Thus, this technique does not intrinsically allow us to overcome undesirable mechanical effects such as the variation in external longitudinal forces (when a measurement of hydrostatic pressure is sought) or the variation in hydrostatic pressure (when a measurement of external longitudinal forces, independent of the mechanical effects of hydrostatic pressure, is sought), since the number of physical quantities to be separated (temperature, hydrostatic pressure and longitudinal mechanical deformation) is greater than the number of equations governing the problem.

[0018] Another technique is described in document US 5,841,131. It is also based on the use of a birefringent optical fiber, dedicated mainly to the measurement of the variation of the hydrostatic pressure applied to it, independently of temperature variations. The principle consists of exploiting the separation of the Bragg peak under the effect of the hydrostatic pressure which accentuates the birefringence effect. However, this principle alone does not allow the separation of the two mechanical effects of longitudinal deformation and hydrostatic pressure, independently of the effects of temperature, applied to the optical fiber, because, here again, the problem is poorly posed (number of unknowns to be determined greater than the number of equations) to separate, independently of one another, the three physical quantities in question.The solutions described in applications FR 3 125875 and FR 3 125 879 effectively make it possible to overcome the effects of temperature, independently of the effects of the hydrostatic pressure applied to a pressurized pipe sealed at its ends, but they remain dependent on the variation in the longitudinal forces 6F, generally unknown, which are applied to it.

[0019] The solution described in document FR 3 125 878 provides a partial answer to the measurement of the 6F variation of the longitudinal forces applied to the pressurized pipe, independently of the effects of hydrostatic pressure. But it requires that the measurement technique implemented is itself intrinsically compensated for the effects of temperature (such as, for example, the Brillouin reflectometry measurement technique described in document EP 3 232 165), or that the effects of temperature remain negligible (hypothesis which can be verified in the case of very rapid phenomena, for example in detonation as long as the transducer remains in its elastic deformation domain, and that the thermal exchanges with the surrounding structure remain negligible), or that the temperature remains constant, in the however limiting hypothesis that the transducer does not present any sensitivity to the hydrostatic pressure which is applied to it.

[0020] No combination of the solutions described in documents FR 3 125 875, FR 3 125878 and FR 3 125 879 can solve the problem on its own either, because the different configurations in terms of radial positions (on internal or external surfaces, or in the wall of the structure) and angular orientations of the transducers are largely incompatible with each other. Moreover, none of these solutions takes into account, again, the pressure sensitivity K P transducers which must necessarily be corrected when the wall undergoes a pressure differential P e xt-Pint non-zero between its internal and external faces, since when a transducer is positioned in the thickness of the wall, it is subjected to a hydrostatic pressure which depends on the variations of the internal pressures Pint and external P ext, which must necessarily be taken into account in order not to cause a significant measurement bias on each of the three effects that we are seeking to separate, something that none of the three aforementioned documents have considered so far.

[0021] Finally, despite the possibility of being able to carry out a measurement by optical fiber intrinsically decorrelated from the effects of temperature (using, for example, a measurement by Brillouin reflectometry, as described in document EP 3 232 165), for the implementation of the solution described in document FR 3 125 878, there remains the problem of calibrating such a measurement which natively provides a measurement of a purely mechanical nature only for the optical fiber. However, it is necessary at least to take into account the additional mechanical effects generated on it by the differential expansions with the host structure, which is not always possible to achieve with sufficient precision, in particular if the thermal behavior of the instrumented structure is not known sufficiently precisely in the temperature range considered. In addition to this effect of differential expansions, the sensitivity K Pin hydrostatic pressure of such a measuring technique must, here again, be taken into account, since the optical fiber is positioned in the wall or on the surface of the structure, which neither document FR 3 125 878, nor document EP 3 232 165, deals with satisfactorily.

[0022] The object of the present invention is to propose a device and a method for measuring variations in force (other than that exerted by hydrostatic pressure) and mechanical deformation, hydrostatic pressures, and temperature to which a structure is subjected, overcoming the aforementioned drawbacks, making it possible to carry out a selective measurement of the three components of variations in temperature AT, hydrostatic pressure AP (internal APint or / and external AP ex t) and longitudinal force 6F, independently of each other, provided that the conditions for achieving this are met.

[0023] STATEMENT OF THE INVENTION

[0024] To this end, the invention relates to a non-intrusive (or slightly intrusive) measuring device intended to measure a variation in force according to a predetermined orientation, other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising:

[0025] - a sensor comprising at least one optical waveguide installed integrally on one of the surfaces or in the wall of a cylindrical test body, of circular section, hollow and sealed at its ends, deforming in its elastic domain, each optical waveguide locally describing a circular helix positioned at a radius r around the axis of revolution of the test body, and oriented locally at a predetermined angle cjj(r) relative to a plane normal to said axis of revolution, each waveguide carrying at least one transducer whose mechanical component of the measurement is sensitive to the orientation and configured to carry out a selective measurement of a first primary variable, the true relative variation of which is representative of a local variation of hydrostatic pressure applied to the test body or of a second primary variable,whose true relative variation is representative of a local variation of longitudinal force, other than exerted by hydrostatic pressure, applied to the test body, the selectivity of one or the other mechanical effect (hydrostatic pressure vs. longitudinal force), by means of the true relative variations of the first and second primary variables, being ensured by the angular orientation $ of each waveguide, and,

[0026] - a calculator configured to selectively calculate the local variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, and / or the local variation of the hydrostatic pressure AP applied to the test body, as a function of the true relative variations of the measurements of said first and / or second primary variables.

[0027] This device makes it possible to separate the two mechanical effects exerted by a hydrostatic pressure and a longitudinal force (distinct from that exerted by a hydrostatic pressure) applied to the test body, independently of each other, independently of the shear Erz (according to its radius r and its axis of revolution (zz)) which this test body can undergo.

[0028] It will be noted that the expression "waveguide carrying a transducer" means, depending on the embodiment of the invention, that a transducer is inscribed in the waveguide or that the waveguide itself carries or has the function of transducer.

[0029] Advantageously, the calculator is further configured to calculate the local variation of the temperature AT as a function of the true relative variations of the measurements of said first and / or second primary variables, since the primary measurement is sensitive to the effects of temperature.

[0030] Thus, the device allows to separate the temperature, in addition to the two mechanical effects of hydrostatic pressure and longitudinal force, other than exerted by hydrostatic pressure.

[0031] Advantageously, the calculator is configured to calculate the local variation of the longitudinal mechanical deformation AE meCcap of the test body as a function of the local variation of the longitudinal force 6F (other than exerted by hydrostatic pressure) and the local variation of hydrostatic pressure AP applied to the test body, as well as the physical parameters of the test body.

[0032] Advantageously, the device comprises at least one pair of optical waveguides oriented locally in a circular helix around the axis of revolution of the test body and carrying at least one pair of transducers, the optical waveguides of each pair being positioned according to two radii ri and distinct around the axis of revolution of the test body, and oriented locally according to a pair of predetermined angles relative to a plane normal to said axis of revolution. Thus, the device has a selective nature of the measurement of the variation of the hydrostatic pressure and / or of the variation of the longitudinal forces, other than those exerted by a hydrostatic pressure, independently of the effects of the temperature, with the additional provision of the indication of the local variation of the temperature since the primary measurement provided by each transducer is itself sensitive to the temperature.

[0033] In addition, the local circular helical orientation of the transducers ensures, by construction, that they are totally insensitive to shears of the type according to the radius r and the axis of revolution (zz)) undergone by the test body, as may for example be the case when this test body is housed within a deformable host structure, which makes it possible to ensure, in this way, a particularly robust measurement of the variation of the longitudinal forces 6F.

[0034] According to a first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body according to first and second angles distinct by relative to a plane normal to the axis of revolution, the first optical waveguide being dedicated to measuring the variation of the hydrostatic pressure AP, the second optical waveguide being dedicated to measuring the variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body. This can be achieved by exploiting a continuously sensitive distributed measurement technique, intrinsically temperature compensated, such as for example the Brillouin reflectometry measurement technique based on the Landau-Placzek ratio, described in document EP 3 232 165 B1 or in the article doi: 10.1109 / 3.663443, with a hydrostatic pressure sensitivity K P now taken into consideration, which is new compared to previous approaches (notably FR 3 125875, FR 3 125 878 and FR 3 125879).

[0035] According to variants of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body according to the same family of angles ou P ar relative to a plane normal to the axis of revolution of the test body, the first family of angles being dedicated to the selective measurement of the variation in hydrostatic pressure AP, while the second family of angles is dedicated to the selective measurement of the variation in the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body. More particularly, according to a variant of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body, according to first and second angles P arrelative to a plane normal to the axis of revolution of the test body, these two angles being equal if the waveguides are both positioned in the wall of the test body or positioned on the internal and external surfaces, said first and second optical waveguides being dedicated to the measurement of the variation in hydrostatic pressure AP (internal APjnt or external AP ex t) to the test body. The angles take a first identical and constant value in the wall of the test body and a second identical and constant value on the internal and external surfaces of the test body, the first and second angle values ​​being distinct.

[0036] According to another variant of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body, according to first and second angles <p5 t distinct with respect to a plane normal to the axis of revolution of the test body, said first and second optical waveguides being dedicated to measuring the variation of the longitudinal force 6F, other than exerted by hydrostatic pressure, applied externally to the test body.

[0037] According to a second embodiment, the device comprises first and second pairs of optical waveguides positioned locally in a circular helix around the axis of revolution of the test body according to a first pair of distinct radii and a second pair of distinct rays the two waveguides of the first pair are positioned locally according to first and second angles P ar report to a plane normal to the axis of revolution, these two angles being equal if the waveguides are both positioned in the wall of the test body or positioned on the internal and external surfaces, while the two waveguides of the second pair are positioned locally at two distinct angles P ar relative to a plane normal to the axis of revolution, the first pair of waveguides being dedicated to measuring the variation of the hydrostatic pressure AP (internal APint or external AP ex t), while the second pair of waveguides is dedicated to measuring the variation of the longitudinal force 6F, other than exerted by hydrostatic pressure, applied externally to the test body. This allows the simultaneous selective measurement of the two mechanical effects of hydrostatic pressure variation AP (internal APint or external AP ext) and variation of longitudinal forces 6F, other than those exerted by hydrostatic pressure, applied externally to the test body relative to an arbitrary reference state, as well as the local variation in temperature AT of the test body since the primary measurement provided by each transducer is itself sensitive to temperature.

[0038] According to a third embodiment, the device comprises a single optical waveguide positioned at a predetermined radius in the elastic wall of the test body or on the internal or external surface thereof, and oriented locally in a circular helix around the axis of revolution of the test body at a predetermined angle relative to a plane normal to the axis of revolution, the optical waveguide being dedicated to measuring the variation in hydrostatic pressure AP (internal APint or external AP ext) or to the measurement of the variation of the longitudinal force 6F, other than exerted by hydrostatic pressure, applied externally to the test body, by using a continuously sensitive and self-compensated temperature distributed measurement technique, such as, for example, the Brillouin reflectometry measurement technique based on the Landau-Placzek ratio, described in document EP 3 232 165 Bl.

[0039] According to a fourth embodiment, the device comprises first, second and third optical waveguides oriented locally in a circular helix around the axis of revolution of the test body according to first, second and third radii ri, r2 and r3 of which at least two of them are distinct, and according to any first, second and third angles but in absolute value distinct modulo n for at least two of them, cf(ri), <t»(r2) et cftra), par rapport à un plan normal à l'axe de révolution, les premier, deuxième et troisième guides d'ondes optiques étant dédiés à la mesure sélective de la variation de pression hydrostatique AP (interne APint ou externe AP ex t) and the variation of the longitudinal force 6F, other than exerted by hydrostatic pressure, applied to the test body.

[0040] Advantageously, according to a first aspect of the present invention, each optical waveguide carries a Bragg grating type transducer for carrying out distributed measurements (equivalent English term: quasi-distributed measurements), adapted for carrying out very localized measurements, this Bragg grating being able to be of high order (for example greater than 500) in order to present a frequency comb in the spectral domain, and thus conduct a more precise measurement by simple averaging of the frequency shift of each of its resonances.Advantageously, according to another aspect of the present invention, each optical waveguide carries a transducer according to a continuously sensitive reflectometric technique of the Brillouin type, OFDR (Optical Time Domain Reflectometer) Rayleigh, or phase-OTDR (c[)-OTDR (Optical Frequency Domain Reflectometer) or DAS (Dynamic Acoustic Sensing) adapted to carry out distributed measurements (equivalent English term: distributed measurements) along the optical waveguide.

[0041] Advantageously, according to a first particular aspect of the present invention, the sensor comprises said cylindrical test body, of circular section, delimiting a sealed cavity.

[0042] The sensor is intended to be installed in any host structure, the variation of the external hydrostatic pressure AP ext applied to the test body, and the temperature variation ATi of the test body associated with this variation in hydrostatic pressure, as well as the variation in the longitudinal force 8F &Pext , other than exerted by hydrostatic pressure, applied to the test body, and the temperature variation AT2 of the test body associated (ATi = AT 2 when the assumptions of the underlying model are respected) with this variation in longitudinal force, being defined according to the following equations:

[0043] [Math 1] performed by the transducer) between its reference value T o and its current value: T = T o + A 'P, E is the Young's modulus of the test body, v is the Poisson's ratio of the test body, K P , K £ and K Tare respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation and in temperature of the transducer integral with the host structure (equation (46) of the article doi: 10.3389 / fsens.2022.835140) for the measurement technique considered, APint is the variation of the internal hydrostatic pressure of the test body, and r0, r Oext are respectively the internal and external radii of the test body in its reference state.

[0044] Advantageously, the test body is a micro-structured optical fiber forming a micro-capillary sealed at its ends.

[0045] Advantageously, the test body is coated with a deformable mechanical sheath of polymer type, for example, but not limited to, polyimide or polyacrylate, and more generally, with a sheath capable of transmitting the stresses of the host structure to the transducers secured to the test body.

[0046] Advantageously, the sensor is configured to exploit a birefringence effect of the optical waveguide.

[0047] Advantageously, according to a second particular aspect of the present invention, the host structure has a cylindrical shape, of circular section, hollow and sealed at its ends, itself playing the role of test body. The variations of the internal hydrostatic pressures APint and external AP ex t, the variations of the longitudinal forces ôF^p int and 8F^p ext associated, other than exerted by hydrostatic pressure, and the local temperature variations ATi, AT2, AT3, AT4associated with it which are applied to it (ATi = AT2 = AT3 = AT4when the assumptions of the underlying model are respected), are defined according to the following equations, since the structure deforms in its elastic domain, with transducers positioned in the wall at radii ri and r2:

[0048] [Math 3]

[0049] [Math 5]

[0050] [Math 6] performed by the transducer) between its reference value T o and its current value: T = T o + AT, E is the Young's modulus of the structure, v is the Poisson's ratio of the structure, K P , K £ and K T are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation and in temperature of the transducer, integral with the host structure for the measurement technique considered (for example Bragg grating type), APint is the variation of the internal hydrostatic pressure, AP ex t is the variation of the external hydrostatic pressure, and r0, r Oext are respectively the internal and external radii of the cylindrical structure in its reference state.

[0051] The invention also relates to an installation comprising:

[0052] - a structure whose pressure and / or mechanical deformation and / or temperature are to be monitored, and

[0053] - a measuring device according to any of the above characteristics.

[0054] Advantageously, according to a first particular aspect of the present invention, the structure of the installation has a cylindrical shape, of circular section, hollow and closed at its ends. This structure then plays the role of the test body of the sensor.

[0055] Advantageously, according to a second particular aspect of the present invention, the structure has any shape, and the sensor, comprising a cylindrical test body, of circular section, hollow and sealed at its ends, is housed in a perfectly integral manner within the structure or on the surface thereof.

[0056] The invention also relates to a non-intrusive method for measuring a variation in longitudinal force (other than exerted by hydrostatic pressure) and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising the following steps: - positioning at least one optical waveguide locally describing a circular helix on one of the surfaces or in the wall of a cylindrical test body, of circular section, hollow and sealed at its ends, each optical waveguide being positioned at a radius r around the axis of revolution of the test body and being oriented locally according to a predetermined angle <t»(r) par rapport à un plan normal au dit axe de révolution, chaque guide d'onde portant au moins un transducteur sensible à l'orientation,

[0057] - carry out, by means of the primary measurement of said transducer, a selective measurement of a first mechanical quantity representative of a local variation in hydrostatic pressure applied to the test body or of a second mechanical quantity representative of a local variation in longitudinal force, other than exerted by hydrostatic pressure, applied to the test body, the selectivity of one or other of the first and second mechanical quantities being ensured by the orientation of each waveguide, and

[0058] - selectively calculating the local variation of the longitudinal mechanical deformation of the test body and / or the local variation of the hydrostatic pressure applied to the test body as a function of the measurement of said first and / or second primary measurements.

[0059] BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The invention will be better understood with the aid of the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0061] [Fig. 1] illustrates a low-intrusive measuring device intended to measure a variation of a longitudinal force (along the orientation k of the axis of revolution (zz) of the sensor test body), other than exerted by a hydrostatic pressure, and / or a variation of hydrostatic pressure relative to a host structure of interest, according to an embodiment of the invention;

[0062] [Fig. 2A], [Fig. 2B], [Fig. 2C], [Fig. 2D], [Fig. 2E] and [Fig. 3A], [Fig. 3B] each illustrate a low-intrusive measuring sensor intended to measure a variation of a longitudinal force (along the orientation k of the axis of revolution (zz) of the sensor test body), other than exerted by a hydrostatic pressure, and / or a variation of hydrostatic pressure relative to a host structure of interest, according to different embodiments of the invention;

[0063] [Fig. 4] is a flowchart illustrating the steps of a method for the low-intrusive measurement of a longitudinal mechanical deformation (Le.: along the orientation k of the axis of revolution of the sensor test body) and / or of a variation in hydrostatic pressure relating to a structure of interest, according to the embodiments of Figs. 1, 2A-2E and 3A-3B;

[0064] [Fig. 5] is a flowchart illustrating the steps of a method for the low-intrusive measurement of a longitudinal mechanical deformation (Le.: along the orientation k of the axis of revolution of the sensor test body) and / or of a variation in hydrostatic pressure relating to any structure of interest, according to a particular embodiment of the invention;

[0065] [Fig. 6] is a flowchart illustrating the steps of a method for the low-intrusive measurement of a longitudinal mechanical deformation (Le.: according to the orientation k of the axis of revolution of the sensor test body) and / or of a pressure variation relating to any structure of interest, according to another particular embodiment of the invention;

[0066] [Fig. 7A], [Fig. 7B] each illustrate a low-intrusive measuring sensor intended to measure a variation in a longitudinal force (along the orientation k of the axis of revolution of the sensor test body), other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relative to a host structure of interest, according to different embodiments of the invention;

[0067] [Fig. 8A], [Fig. 8B] each illustrate a low-intrusive measuring sensor intended to selectively measure, with or without exploitation of birefringence, the variation in hydrostatic pressure AP (internal APint or / and external AP ex t) and the variation of the longitudinal force 6F (according to the orientation k of the axis of revolution (zz) of the test body of the sensor), other than exerted by a hydrostatic pressure, applied to the test body, according to particular modes of the invention.

[0068] DETAILED DESCRIPTION

[0069] The concept underlying the invention is based on the selectivity of mechanical effects by means of the specific orientations of the transducers, the mechanical component of the primary measurement of which is sensitive to the orientation, coupled with their radial positions in the wall or on the surface of the test body, making it possible to overcome one or the other mechanical effect depending on the orientation in question, thus reducing the complexity of the underlying thermomechanical problem (and consequently of the associated solutions) to the resolution of only two independent equations, requiring the implementation of only two transducers since their measurement is sensitive to temperature, since in the most general case where the orientation of the transducers is arbitrary, the problem is described by three independent equations, then requiring the implementation of three transducers (the two mechanical effects of hydrostatic pressure and longitudinal force,other exerted by hydrostatic pressure, then being obtained simultaneously, in addition to the temperature information since the measurement provided by the transducers is sensitive to this parameter).,

[0070] Fig. 1 illustrates a non-intrusive measuring device for measuring a variation in a longitudinal force, other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relative to a host structure of interest, according to one embodiment of the invention.

[0071] Such a measuring device 1 is particularly suitable for measuring a variation in hydrostatic pressure, mechanical force and temperature, in installations comprising pressurized structures, such as, for example, fluid tanks or pressurized pipes. The device is also suitable for measuring variations in hydrostatic pressure, mechanical force other than exerted by hydrostatic pressure, and temperature, in certain structures of turbomachines, power plants, nuclear power plants, etc.

[0072] The measuring device 1 comprises a sensor 3, and an optoelectronic module 5. The sensor 3 comprises at least one optical waveguide 7 intended to be installed integrally on one of the surfaces or in the wall of a cylindrical test body 9, of circular section, hollow and sealed at its ends, deforming in its elastic domain, and extending along an axis of revolution (zz) (Le.: orientation along k). A single optical waveguide 7 is shown in the example of Fig. 1 but of course, the measuring device 1 can comprise several (see the other figures). Each optical waveguide 7 locally describes a circular helix positioned at a radius r around the axis of revolution (zz) of the test body and oriented locally according to a predetermined angle <t»(r) par rapport à un plan normal à l'axe de révolution (zz). On notera qu'un angle égal à ± n / 2 (modulo n) est synonyme d'orientation selon cet axe de révolution (zz).

[0073] Each optical waveguide 7 carries at least one transducer (not shown) whose mechanical component of the measurement is sensitive to the orientation. According to a first aspect of the invention, the optical waveguide 7 carries at least one Bragg grating type transducer, suitable for carrying out distributed measurements. According to a second aspect of the invention, the optical waveguide 7 carries at least one transducer according to a continuously sensitive reflectometric technique of the Brillouin type (including the measurement technique described in document EP 3 232 165), OFDR Rayleigh or even phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing) suitable for carrying out measurements distributed along the optical waveguide. According to this second aspect, the optical waveguide 7 itself plays the role of transducer.

[0074] Thus, according to a first aspect, the transducer can be inscribed in the optical waveguide 7 such as a Bragg grating. According to a second aspect, the transducer is intrinsically carried by the optical waveguide 7 to carry out measurements by Brillouin reflectometry (according to the measurement technique described in document EP 3 232 165), OFDR Rayleigh or even c|)-OTDR or DAS, etc.

[0075] Each transducer is configured to perform a selective measurement of a mechanical effect according to a first primary measurement whose true relative variation is representative of a variation in hydrostatic pressure applied to the test body 9 or of a second primary measurement whose true relative variation is representative of a variation of a longitudinal force, other than exerted by hydrostatic pressure, applied to the test body 9. The selectivity of one or other of the first and second mechanical effects (hydrostatic pressure vs. longitudinal force), by means of the true relative variations of the first and second primary variables, being ensured by the orientation of each waveguide 7.

[0076] Advantageously, according to a particular aspect of the present invention, any cylindrical host structure, of circular section, under hydrostatic pressure, sealed and deforming in its elastic domain, such as a storage tank or a pressurized pipe, can be considered as a test body 9. In this case, each optical waveguide 7 carrying the transducer is positioned in the wall of the host structure or on one of its surfaces, which is then itself considered as the sensor 3.

[0077] Furthermore, in the case where the deformable host structure does not have a cylindrical shape, then, according to another particular aspect of the present invention, the sensor 3 intrinsically comprises a cylindrical test body 9, of circular section, hollow and sealed at its ends, deforming in its elastic domain. Advantageously, the test body 9 is a micro-structured optical fiber having, in the thickness of its wall, at least one optical waveguide 7, preferably single-mode, oriented locally in a circular helix around its axis (zz), according to the predetermined angle $ relative to a plane normal to the axis (zz) of the optical fiber. The transducer can then be photo-written in the waveguide 7. In this case, the sensor 3, deforming in its elastic domain, can then be integrated in a solid manner at the very heart of the host structure (in its wall) or on one of its surfaces.It will be noted that the watertight closure of the test body 9 can be achieved, for at least one of its ends, by the instrumented host structure in question when the sensor 3 is embedded in its wall.

[0078] The optoelectronic module 5 comprises a light source 13, an optical spectrometer 15 and a computer 17. The light source 13 is advantageously of the broadband type including the interrogation wavelength ranges for each transducer. The optical spectrometer 15 is adapted to detect and characterize (in power, wavelength, and if necessary, in phase) the signal reflected or backscattered by the transducers 11.

[0079] The computer 17 is configured to control the light source 13 and the optical spectrometer 15, and to interrogate and recover (digitize) the signals from the transducers.

[0080] The calculator 17 is configured to selectively calculate the local variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body 9 and / or the local variation of hydrostatic pressure (internal and / or external) applied to the test body 9 as a function of the true relative variations of the first and / or second primary measurements. The calculator 17 is also configured to calculate the local variation of temperature from the true relative variations of the first and / or second primary measurements, since these are sensitive to temperature.

[0081] Furthermore, the calculator 17 is configured to calculate the local variation of the longitudinal mechanical deformation of the test body 9 as a function of the variations local forces of the longitudinal force 6F (other than exerted by hydrostatic pressure) and of the hydrostatic pressure AP applied to the test body 9, as well as the physical parameters of the test body 9.

[0082] Advantageously, the calculator 17 determines, from a formal model, the variations in longitudinal mechanical deformations, hydrostatic pressures and temperatures applied to the test body 9, thus allowing easy calculation of these quantities.

[0083] Figs. 2A-2E and 3A-3B each illustrate a non-intrusive measuring sensor intended to measure a variation in longitudinal force (according to the orientation k of the sensor test body), other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relative to a host structure of interest, according to different embodiments of the invention. Figs. 2A-2E illustrate a first embodiment while Figs. 3A-3B illustrate a second embodiment, according to different variants.

[0084] It will be noted that the sealed closure of the test body is effective in all the embodiments, even if, for simplification, it is not shown in the diagrams. These different embodiments each relate to a sensor 3 comprising at least one pair of optical waveguides 7a, 7b oriented locally in a circular helix around the axis of revolution (zz) of the test body 9. Each optical waveguide 7a, 7b is positioned along a distinct radius around the axis of revolution (zz) of the test body 9, and oriented locally at predetermined angles relative to a plane normal to said axis of revolution.

[0085] The test body 9 has an empty space inside its wall, and can receive a fluid under pressure in the variant where it is the structure which plays the role of test body 9.

[0086] More particularly, Fig. 2A illustrates a first embodiment according to which the test body 9 (micro-structured fiber, or even reservoir or pressurized pipe) has, in the thickness of its wall, a pair of optical waveguides 7a, 7b carrying a pair of transducers 11a, 11b.

[0087] The first and second optical waveguides 7a, 7b are locally oriented in a circular helix around the axis of revolution according to the angles ttj(r ÛP ) and 4>(r6 F ) relative to a plane normal to the axis of revolution (zz) of the test body 9. The two optical waveguides 7a, 7b are positioned respectively at r AP and rs F in the elastic wall and / or on the surface of the test body 9.

[0088] The measurement technique then implemented makes it possible to provide a primary measurement of a purely mechanical nature, which can be achieved in at least three configurations:

[0089] - provided that the temperature remains constant or varies negligibly, so that its effect on the primary measurement carried out by the transducer remains negligible compared to the desired mechanical effect,

[0090] - during very rapid events, such as detonation, as long as the transducer remains in its elastic deformation domain, and the thermal exchanges with the surrounding structure have effects which can be considered negligible compared to the desired mechanical effect,

[0091] - or when the measurement technique is intrinsically self-compensated in temperature, to provide separately from a single transducer, a measurement of longitudinal mechanical deformation and temperature, such as, for example, measurement by Brillouin reflectometry based on the Landau-Placzek ratio.

[0092] It is recalled that the test body 9 is a hollow cylinder, of circular section, closed at its ends to form a sealed cavity (micro-structured fiber in the case of an optical fiber, or even a tank or pressurized pipe, provided that they are of circular section), deforming in its elastic domain.

[0093] The measurement of the mechanical deformation carried out by each transducer 11a, 11b is sensitive to their orientation according to the two families of specific angles 4JAP and as well as their radial position in the wall or on the surface of the test body 9. These angles are dependent on the sensitivities to mechanical deformation and hydrostatic pressure of the transducers 11a, 11b, and possibly on their radial position in the wall or on the surface of the test body. On the other hand, the orientation of the transducers 11a, 11b, according to each of the two families of angles, is in no way dependent on the temperature sensitivity of the transducer. This orientation is solely dependent on the mechanical characteristics (Young's modulus and Poisson's ratio) and geometrical characteristics (internal and external radii) of the test body, where applicable, on the radial position of the transducer (in the wall or on the surface), as well as the sensitivities to longitudinal mechanical deformation, and, where applicable, to hydrostatic pressure, of the transducer.

[0094] Depending on whether one wishes to carry out a measurement of variation in hydrostatic pressure or longitudinal force, other than exerted by hydrostatic pressure, the two waveguides 11a, 11b are positioned at two angles at 4MP and <t»6F distincts en valeur absolue modulo n (4JAP * ± <t>6F mod n) relative to the axis (zz) of the test body 9.

[0095] The properties of the test body 9 (Le.: cylindrical, of circular section, hollow and sealed at its ends) give it such a behavior (in response to the hydrostatic pressure and longitudinal forces, distinct from those exerted by a hydrostatic pressure, which are applied to it) that a directional measurement, carried out by transducers 11a, 11b which are thermomechanically integral with it, does not present the same sensitivity to these two effects depending on the orientation of these transducers and their radial position in the wall or on the surface of the test body. The selectivity of one or the other of these two mechanical effects (in other words obtained independently of each other) is ensured by the choice of the angle (<|3AP OR 4Î6F) in question, the residual sensitivity to the desired mechanical effect (hydrostatic pressure vs.longitudinal force, other than exerted by hydrostatic pressure) being mainly obtained by the distinct radial positions of the two transducers.

[0096] The selectivity of the mechanical effects is thus the result of the specific orientations of the transducers 11a, 11b making it possible to overcome one or the other effect depending on the direction in question. This selectivity is based on the exploitation of the Poisson transverse contraction effect. It is this Poisson effect which makes it possible to explain that the component of the mechanical deformation of the test body 9 changes sign from the direction of application of the longitudinal force applied to it (which we are trying to overcome) to its perpendicular direction, since it passes, by continuity, through a remarkable intermediate angle where its value is zero.It is this remarkable angle which is used to selectively measure the hydrostatic pressure applied to the test body 9 on the one hand, and its complementary angle to selectively measure the longitudinal force, distinct from that exerted by a hydrostatic pressure, which is applied to it on the other hand.

[0097] The intrinsic compensation of the effects of temperature, since the measurement technique implemented is not itself self-compensated in temperature, is the result of the difference in the true relative variations of two primary measurements obtained from two transducers oriented according to the same family of angles and positioned at two distinct radii, within the wall or on the surface of the test body, since by hypothesis and construction, the two transducers are subjected to the same temperature.

[0098] Also, the local variation of the temperature AT is additional information provided by the sensor 3 in all embodiments, since the transducers have a non-zero sensitivity to the temperature, or the measurement technique implemented is itself self-compensated in temperature, since it generally provides in a dual manner, the temperature or its variation relative to an arbitrary reference for the transducer considered (as is the case, for example, for the measurement technique by Brillouin reflectometry based on the Landau-Placzek ratio, described in the document EP 3 232 165).

[0099] Furthermore, in the case of a sensor 3 which can be integrated into the heart of a structure of any geometry, the hydrostatic pressure, by the gradient of mechanical deformations which it creates in the thickness of the wall, induces a birefringence effect which can also be exploited for selective measurements of variations in hydrostatic pressure and longitudinal forces, other than those exerted by hydrostatic pressure.

[0100] Fig. 2B is a variant of the first embodiment illustrating a sensor intended to measure, with or without exploitation of birefringence, the variation of hydrostatic pressure AP applied to the sensor.

[0101] The sensor 3, according to this second embodiment, comprises first and second optical waveguides 7a, 7b oriented locally in a circular helix around the axis of revolution (zz) of the test body 9 at an angle 4MP relative to a plane normal to the axis of revolution of the test body 9, the value of which depends on their radial position (on the surface

[0102] - internal or external - or in the thickness of the test body). The two optical waveguides 7a, 7b are positioned respectively at the radii and r2, p in the elastic wall of the test body 9 and / or on its surfaces. The two optical waveguides 7a, 7b carry two transducers 11a, 11b, respectively of the Bragg grating type.

[0103] The two transducers 11a, 11b are preferably positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature variation in the event that there is a temperature gradient along the test body.

[0104] The specific orientation of the two transducers, according to this angle 4JAP, allows them to remain insensitive to variations in longitudinal forces 6F, other than those exerted by hydrostatic pressure, applied to the test body 9, while their sensitivity to mechanical deformation, under the effect of the variation in hydrostatic pressure AP, is mainly modulated by their distinct radial positions in the wall of the test body.

[0105] The difference in true relative variations, compared to an arbitrary reference state, between the two primary measurements of the transducers, subjected by hypothesis to the same temperature, then eliminates the effect of temperature variations, with a result of a purely mechanical nature, in direct relation with the variation in hydrostatic pressure AP, which makes it possible to ensure the selective nature of their measurement, independently of the effects of temperature, and by extension, of any other phenomenon of a non-mechanical nature such as the effects of ionizing radiation.

[0106] And since the transducers have a non-zero sensitivity to temperature, the local temperature variation AT is additional information provided by the sensor 3, since the temperature is the only non-mechanical phenomenon to which the transducers are subjected, obtained jointly during the formal resolution of the underlying thermomechanical problem.

[0107] Fig. 2C is another variant of the first embodiment, also for selectively measuring, with or without exploitation of birefringence, the variation of the hydrostatic pressure AP applied to the sensor 3.

[0108] According to this variant, the two waveguides 7a, 7b are exploited by a distributed measurement reflectometric technique on optical fiber, sensitive to both temperature and mechanical deformation, such as the Brillouin, OFDR Rayleigh, phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0109] Fig. 2D is yet another variant of the first embodiment illustrating a sensor intended to selectively measure, with or without exploitation of birefringence, the variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, according to the orientation k of the sensor.

[0110] The sensor 3 according to this third embodiment, comprises first and second optical waveguides 7a, 7b oriented locally in a circular helix around the axis of revolution (zz) of the test body at angles distinct with respect to a plane normal to the axis of revolution of the test body 9. The two optical waveguides 7a, 7b are positioned respectively at radii r lgF and r 2gF distinct in the elastic wall of the test body 9. The two optical waveguides 7a, 7b carry transducers 11a, 11b of the Bragg grating type.

[0111] The two transducers 11a, 11b are preferably positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature variation in the event that there is a temperature gradient along the test body.

[0112] The specific orientation of the two transducers, depending on the angles And <P5F(T2 5F ), allows them to remain insensitive to variations in the hydrostatic pressure AP applied to the test body 9, while their sensitivity to mechanical deformation, under the effect of the variation in longitudinal forces 6F (distinct from those exerted by hydrostatic pressure), is modulated by their distinct radial positions in the wall or on the surface of the test body.

[0113] The difference in true relative variations, compared to an arbitrary reference state, between the two primary measurements of the transducers, subjected by hypothesis to the same temperature, then eliminates the effect of temperature variations, with a result of a purely mechanical nature, in direct relation with the variation of longitudinal forces 6F (distinct from those exerted by hydrostatic pressure), which makes it possible to ensure the selectivity of their measurement, independently of the effects of temperature, and by extension, of any other phenomenon of a non-mechanical nature such as the effects of ionizing radiation.

[0114] And since the transducers have a non-zero sensitivity to temperature, the local temperature variation AT is additional information provided by the sensor 3, since the temperature is the only non-mechanical phenomenon to which the transducers are subjected, obtained jointly during the formal resolution of the underlying thermomechanical problem. Fig. 2E is yet another variant of the first embodiment, also for selectively measuring, with or without exploitation of birefringence, the variation in longitudinal force 6F, other than exerted by hydrostatic pressure, according to the orientation k of the sensor.

[0115] According to this variant, the two optical waveguides 7a, 7b are operated by a distributed measurement reflectometric technique on optical fiber, sensitive to both temperature and mechanical deformation, such as the Brillouin, OFDR Rayleigh, phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0116] Fig. 3A illustrates a second embodiment according to which the test body (micro-structured fiber, reservoir, or even pressurized pipe) has, in the thickness of its wall and / or on its surfaces, two pairs of optical waveguides 7a, 7b, 7c, 7d carrying two pairs of transducers 11a, 11b, 11c, 11d.

[0117] More particularly, the sensor 3 comprises first 7a, 7b and second 7c, 7d pairs of optical waveguides locally describing two pairs of circular helices carrying two pairs of transducers 11a, 11b, and 11c, 11d. A first pair of waveguides 7a, 7b is dedicated to measuring the variation of the hydrostatic pressure AP, while the second pair of waveguides 7c, 7d is dedicated to measuring the variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body 9, according to the orientation k of the sensor. This makes it possible, with or without exploitation of birefringence, to selectively measure the two mechanical components of the variation of hydrostatic pressure AP and the variation of the longitudinal force 6F (other than exerted by a hydrostatic pressure) applied to the sensor 3.

[0118] The two waveguides 7a, 7b of the first pair, locally oriented in a circular helix, are positioned around the axis of revolution at the angle 4MP relative to a plane normal to the axis of revolution of the test body 9. The two waveguides 7c, 7d of the second pair of waveguides, locally oriented in a circular helix, are positioned around the axis of revolution at the angles <p5 relative to a plane normal to the axis of revolution. The first 7a, 7b and second 7c, 7d pairs of waveguides are positioned respectively at r ± , r 2&p , and r lg , r 2gF in the elastic wall of the test body 9, each carrying a transducer 11a, 11b, 11c, 11d, of the Bragg grating type.

[0119] The combination of these two families of angles, using two pairs of transducers positioned within the same test body 9, allows the device 1 to carry out a simultaneous selective measurement of the two mechanical effects of hydrostatic pressure variation AP (internal APint or / and external AP ex t) and variation of longitudinal forces 6F, other than those exerted by hydrostatic pressure, applied to the test body. Subsequently, variations of longitudinal mechanical deformations A£ meCcap , depending on the orientation k of the sensor, relative to an arbitrary reference state, can be deduced from it.

[0120] Fig. 3B is a variant of the second embodiment also for measuring the variation of hydrostatic pressure AP applied to the sensor, as well as the variation of the longitudinal force 6F, according to the orientation k of the sensor.

[0121] According to this variant, the four waveguides 7a, 7b, 7c, 7d are exploited by a distributed measurement reflectometric technique on optical fiber, sensitive to both temperature and mechanical deformation, such as the Brillouin, OFDR Rayleigh, phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0122] Figs. 4, 5 and 6 illustrate the use by the computer of a thermomechanical model to calculate, from a formal model derived from this model, the variations in longitudinal mechanical deformations (according to the orientation k of the sensor), hydrostatic pressures and temperatures relative to the sensor according to different embodiments of the invention.

[0123] Fig. 4 is a flowchart illustrating the steps of a non-intrusive method for measuring a variation in mechanical deformation and / or a variation in hydrostatic pressure relating to a structure of interest, according to the embodiments of Figs. 1, 2A-2E and 3A-3B.

[0124] Step E1 concerns the instrumentation of the host structure with one or more measuring devices 1 each comprising at least one optical waveguide 7 according to the embodiments of Figs. 1, 2A-2E and 3A-3B.

[0125] The optical waveguides 7 are positioned within the test body 9 forming the sensor 3. In the case where the host structure has a suitable cylindrical geometry shape, and provided that it is sealed at its ends, it can itself act as a test body 9 as soon as it deforms in its elastic domain. Alternatively, in the case of a host structure of any geometry, a test body 9 is integrated integrally within the wall of the structure, or on one of its surfaces.

[0126] In step E2, the transducer of each optical waveguide 7 provides first primary measurements and / or second primary measure whose difference of the true relative variations AT, and A^ P ar relative to an arbitrary reference state is representative, in a selective and exclusive manner, of a local variation of a hydrostatic pressure AP (internal or external), or of a local variation of a longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body. The selectivity of one or the other mechanical effect (hydrostatic pressure AP vs. longitudinal force 6F) achieved by first and / or second primary measurements is ensured by the orientation $ of the transducers concerned.

[0127] In the case where the measurement technique is sensitive to temperature, and the effect of temperature on the strain measurement is not self-compensated (e.g., measurement by Bragg gratings) and the effect of temperature on the transducers cannot be neglected, the number of transducers is at least two, and the true relative variations of the primary measurements 4% and 4^2 must be selective of the same mechanical effect (variation of hydrostatic pressure AP or, exclusively, of longitudinal force 6F, distinct from that exerted by hydrostatic pressure), i.e. oriented along the same family of angles.

[0128] In the case where the mechanical deformation measurement technique is by nature insensitive to temperature (self-compensated measurement), such as for example the distributed measurement technique by Brillouin reflectometry based on the Landau-Placzek ratio, described in document EP 3 232 165, or where the effect of temperature on the transducer can be neglected, at least a single waveguide (or transducer) is necessary, oriented according to its selective angle family for the measurement of the mechanical effect considered, provided that the conditions for applying such a measurement are however met (the selective angle in question must take a real value).

[0129] The calculator 17 interrogates each transducer and selectively calculates the local variation of the longitudinal force 6F (other than exerted by a hydrostatic pressure) applied to the test body 9, or the local variation of internal hydrostatic pressure APint or external AP ex t applied to the test body 9. The calculator 17 further calculates the local temperature variation AT of the test body 9 since the primary measurement is sensitive to temperature.

[0130] The variation of the longitudinal force 6F (other than exerted by hydrostatic pressure) or the local variation of internal hydrostatic pressure APint or external AP ex t is determined based on the true relative variation AT, of the first primary measurement and / or the true relative variation AT^ of the second primary measurement according to the orientation $ of each transducer 7. This calculation is detailed further in relation to Figs. 5 and 6.

[0131] In step E3, the calculator 17 determines the local variation of the longitudinal mechanical deformation of the test body 9 as a function of the longitudinal variations 6F effort (other than exerted by hydrostatic pressure) and variations in internal APint and external AP hydrostatic pressures ex t applied to the test body 9, as well as the physical parameters of the latter. The variation of longitudinal mechanical deformation A£ m ec cap of the sensor, and more particularly of the test body, is given by: [Math 7]

[0132] E is the Young's modulus and v the Poisson's ratio (-1 < v < 0.5) of the test body, r Oext are respectively the internal and external radii of the test body 9 in its reference state.

[0133] In step E4, the computer 17 makes corrections to the variation in longitudinal mechanical deformation A£ meCcap of the sensor 3 calculated in step E3 to match the nature of this measurement to that of the instrumented host structure. These corrections are based on taking into account the differential expansions between the test body 9 and the instrumented host structure, to determine the component of the mechanical deformation variation A£ m ec struct / according to the orientation k of the sensor, of the host structure in question, according to the following expression: [Math 8] where AT is the measure of local temperature variation, and Aa = (a s thing - a cap ) is the difference in thermal expansion coefficients between the host structure and the test body 9. Of course, Aa = 0 in the case where the host structure acts as the test body 9.

[0134] Step E5 is a test to verify whether the host structure acts as a test body or not. If so, we go to step E6. If not, we go to step E8.

[0135] Step E6 concerns the case where the host structure is a tank or a pressurized pipe, of circular section, sealed at its ends, deforming in its elastic domain. In this case, the calculator 17 considers that the variation in mechanical deformation A£ meCstruct is its variation in longitudinal mechanical deformation, as calculated in step E3.

[0136] In step E7, the computer 17 optionally determines the other local components of the variations in the displacements, the strain tensor and the stress tensor for the host structure, which by hypothesis has an isotropic global behavior, and deforms in its elastic domain. Tl

[0137] Step E8 concerns the case where the sensor 3 is embedded or positioned on the surface of the host structure of any nature. At this step, the computer 17 considers that the variation in longitudinal mechanical deformation Af m ec struct calculated in step E4 is the local component of the variation of the mechanical deformation of the host structure, according to the orientation k of the sensor test body, of the micro-structured optical fiber type.

[0138] In step E9, the calculator 17 determines some values ​​of other local components. The calculation is carried out by continuity between the local variations of the components relating to the sensor test body and to the host structure, on their common interface defined by the external surface of the sensor test body.

[0139] It should be noted that local equality by continuity is valid for the following quantities: temperature variation AT, variation of total displacements (mechanical + thermal) Au (radial component), Aw (longitudinal component), total longitudinal deformation A£ totcap (Ae mechanics mec + thermal Ae th ) of the Û£ sensor tot = Ae mec + Ae th with the component, according to the orientation k of the sensor test body, of the variation of total local deformation A£ tnt of the host structure (A£ t t and the variation of the constraint radial Ao rr (corresponding, to the nearest sign, to a variation in hydrostatic pressure) exerted on the external surface of the sensor at the very location where the sensor is positioned.

[0140] Fig. 5 is a flowchart illustrating the steps of a non-intrusive method for measuring a variation in mechanical deformation and / or a variation in hydrostatic pressure relating to any structure of interest, according to a particular embodiment of the invention.

[0141] This embodiment concerns the case of a sensor according to Figs. 1 to 3B in its version which can be integrated into the heart of a structure of any geometry.

[0142] Step Eli concerns the configuration of the sensor 3 and its integration into a host structure 19.

[0143] The sensor 3 comprises a test body 9 and at least two waveguides 7 oriented according to the same family of angles. The test body 9 is cylindrical, of circular section, hollow and sealed at its ends, and deforming in its elastic domain. The sealed closure can advantageously be provided, for at least one of the ends, by the instrumented host structure 19 when the sensor 3 is embedded in its wall.

[0144] The test body 9 may be under internal pressure, or preferably, be at zero pressure (Le.: vacuum). It will be noted that if the test body 9 is not under zero pressure, and if the temperature varies significantly with respect to the phenomenon sought, then the value of the internal pressure can be corrected using the ideal gas law since the temperature is one of the physical quantities measured by the sensor since the transducers are themselves sensitive to temperature.

[0145] Advantageously, the test body 9 is a micro-structured optical fiber, thus forming a micro-capillary. The test body (optical fiber) is preferably made of silica, or even of sapphire AI2O3 (the latter solution allowing the sensor to be used up to approximately 1800°C, with however an overall multimode behavior of the waveguide in the majority of cases, but which can nevertheless still be used with a Bragg grating, with a measurement uncertainty however greater than within a single-mode optical guide).

[0146] In addition, the test body 9, of the optical fiber type, can advantageously be coated with a deformable mechanical sheath, for example made of polymer (polyimide, polyacrylate, etc.), and of low thickness (for example, a few tens of micrometers). This ensures its survival throughout the operating period of the structure and achieves good transduction of the mechanical deformations of the instrumented host structure.

[0147] At least two optical waveguides 7 carrying transducers whose mechanical component of the measurement is sensitive to orientation (such as Bragg gratings in the case of distributed measurements, or quite simply two optical waveguides, preferably single-mode, if these are used in Brillouin reflectometry, OFDR Rayleigh, or even phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing) in the case of distributed measurements), are positioned in the thickness of the test body 9 (for example in the wall of the micro-structured fiber).

[0148] Advantageously, the micro-structured fiber of the sensor 3 can be manufactured by 3D nanoprinting to form an end component of an optical fiber, for example of the multi-core type, at the end of which it can be connected. In such a case, the production of locally circular helices, with angles of opposite signs, is conceivable. The combination (arithmetic mean) of measurements carried out with angles of opposite signs makes it possible to overcome, in a conventional manner, the effects of torsion on the sensor.

[0149] Alternatively, the micro-structured fiber can be manufactured by drawing, on a fiber-drawing lathe, a preform structured in such a way as to have optical waveguides to house the transducers. This preform, once drawn, can undergo, locally or not, one or more twisting operations so as to force the optical waveguides to conform locally into circular helices according to the remarkable angles defined previously or according to any angles distinct in absolute value modulo n, or again, the preform can originally have optical waveguides in the predefined orientations or according to any angles distinct in absolute value modulo n, thus making it possible to limit the number of subsequent local twisting operations.

[0150] Furthermore, in the case of Bragg grating transducers, their photo-inscription can be carried out point-by-point, by femtosecond laser, in each of the optical waveguides 7 arranged locally in a circular helix around the axis of the micro-structured optical fiber 9 (test body).

[0151] The sensor 3, according to the properties described above, allows the measuring device 1 to carry out a selective measurement of the variation in hydrostatic pressure and / or longitudinal forces, other than those exerted by hydrostatic pressure, applied to the test body 9, and then, of its longitudinal mechanical deformations.

[0152] Steps E12 to E17 concern the determination of variations in internal hydrostatic pressure APint or external hydrostatic pressure AP ex t, of the local temperature AT and of the longitudinal forces 6F (according to the orientation k of the sensor), other than those exerted by hydrostatic pressure, depending on the configuration of the transducers (positioned at the radii r according to the families of angles <[>).

[0153] In particular, steps E12 to E16 concern selective measurements in the absence of birefringence (Le.: without separation of the Bragg peak), while step E17 concerns selective measurements in the presence of birefringence.

[0154] Step E12 concerns the selective measurement of the variation in hydrostatic pressure

[0155] APext applying outside the sensor as well as the variation of the local temperature AT associated with the variation of the external hydrostatic pressure.

[0156] In this case, the angles cfi and <t>2 are equal in absolute value to the absolute value of the angle <pm> T modulo n, defined according to their radial position (in the wall or on the surface of the test body) by the following relation: if the transducer is in the wall of the test body:

[0157] [Math 9] modrr whether the transducer is on the internal or external surface of the test body:

[0158] [Math 10] where E is the Young's modulus of the optical fiber test body, K P and K £ are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the transducer, integral with the test body, for the measurement technique considered (for example Bragg grating type), and v is the Poisson's ratio of the test body.

[0159] For example, for a germanosilicate optical fiber: Esince — 72 GPa, Vsiiice — 0.17, and for a Bragg grating transducer: K P —2.87 x 10 -6 MPa -1 and K £ 0.78.

[0160] The variation of external hydrostatic pressure AP ex t is then a linear function fi^Pext de ' a difference of true relative variations: A'Pa — AT b of the primary measures: 'Pg and 'Pb, the true relative variation: A'P of the primary measure: 'P being defined as follows: [Math 11] where A 'P is the variation of the raw value 'P (Le.: primary measurement carried out by the transducer) between its reference value % and its current value 'P (Le.: A 'P = 'P — %).

[0161] Note that for a Bragg grating type transducer 7, the raw value or primary measurement 'P corresponds to its Bragg wavelength: X Br agg. For a measurement by Brillouin reflectometry on an optical fiber (the measurement in this case being of the distributed type, the transducer being the waveguide of the optical fiber itself), the primary measurement 'P corresponds to its Brillouin frequency v B . For a measurement by OFDR Rayleigh reflectometry on an optical fiber (the measurement also being in this case of distributed type, the transducer being the waveguide of the optical fiber itself), the primary measurement 'P corresponds to its Rayleigh frequency v R . For any other fiber optic reflectometry measurement technique (e.g. phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing)), sensitive to temperature and mechanical deformation, the primary measurement 'P is the value of its characteristic quantity v c .

[0162] The variation of hydrostatic pressure AP ex t applied to the external surface of the sensor is given by the following relation: [Math 12]

[0163] Explaining the above formula, the variation of the hydrostatic pressure AP ex t as well as the calculation of the variation of the corresponding local temperature AT are expressed as a function of the configuration of the transducers, in the following manner: if the two transducers are positioned at radii ri and r2 in the wall of the test body:

[0164] [Math 13] if the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0165] [Math 15]

[0166] [Math 16] if the first transducer is positioned at radius ri in the wall and the second transducer on the external surface at radius r Oext of the test body:

[0167] [Math 17]

[0168] [Math 18] if the first transducer is positioned on the internal surface at radius r Q.nt and the second transducer at radius r2 in the wall of the test body: [Math 19]

[0169] [Math 20] where E is the Young's modulus of the optical fiber test body, K P , K £ and K T are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation, and in temperature of the transducer attached to the host structure for the measurement technique considered, APint is the variation of the internal hydrostatic pressure, r Oext are respectively the internal and external radii of the micro-structured optical fiber, acting as a test body, in its reference state, and 'i'ext are respectively the primary measurements of the transducers positioned on the inner surface at radius r0 and on the outer surface at radius r Qext , And and ^2 are respectively the primary measurements of the transducers positioned within the wall, at radii ri and r?.

[0170] Step E13 concerns the selective measurement of the variation in longitudinal forces 6F (other than those exerted by hydrostatic pressure) applied to the test body as well as the calculation of the variation in local temperature AT associated with this variation in longitudinal forces, other than those exerted by hydrostatic pressure.

[0171] The angle cfi is, in absolute value, equal to the absolute value of the angle 4J6F7modulo n, defined by:

[0172] [Math 21] l«Pil = \ <P3F(rt)\ mod7T, r t = r 1; r2, r Q.nt ,r Qext

[0173] In particular, for a selective measurement of the variation of longitudinal forces

[0174] SF^p ext regardless of AP ex t, the angle cfi is, in absolute value, equal to the absolute value of the angle (p$ F .„ (ri) modulo n, defined by the following relation: ext if the two transducers are positioned at radii ri and r2 in the wall of the test body:

[0175] [Math 22] modrr (j = 1,2) if the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0176] [Math 23]

[0177] [Math 24] zx 1 \ r o f (l - 2V)K £ - (r0 2 - r0 2 J / CpE

[0178] < ^PsàfF &AP p ext Gv o ext j = + --2arccos —2 — — - r0 2 5. — nf ( - -l + V)K - £ - - 1 modrr

[0179] The variation of longitudinal forces SF &Pext exerted on the test body is a linear function fsp^p t of the difference of true relative variations: AT a — A'Pj, primary measures

[0180] [Math 25]

[0181] Explicitly, the variation of longitudinal forces SF &Pext and the variation of the local temperature AT are equal to: if the two transducers are positioned at radii ri and r2 in the wall of the test body:

[0182] [Math 26]

[0183] [Math 27] if the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0184] [Math 28]

[0185] [Math 29] if the first transducer is positioned at radius ri in the wall and the second transducer on the external surface at radius r Oext of the test body:

[0186] [Math 30]

[0187] [Math 31] if the first transducer is positioned on the internal surface at radius r0 and the second transducer at radius r2 in the wall of the test body:

[0188] [Math 32]

[0189] [Math 33]

[0190] Step E14 concerns the calculation of the variation in longitudinal mechanical deformation of the test body. Indeed, the variations in internal hydrostatic pressure APint or external APext to the test body 9, the variations in external longitudinal forces 6F applied to the test body (other than those exerted by hydrostatic pressure), and the variations in local temperature AT of the test body, lead to the calculation of the variation in longitudinal mechanical deformation A£ meCcap of the test body sensor 9, according to the following equation: [Math 34] Step E15 concerns the calculation of the component of the variation of the mechanical deformation Ae mPP of the host structure 19 instrumented according to the orientation k of the optical fiber 9. In order to determine this component of variation of mechanical deformation of the host structure, the computer 17 corrects the effects of differential expansions between the host structure 19 and the sensor 3. This correction is based on the local measurement of the variation of the temperature AT (provided jointly by the sensor) and on the difference of the thermal expansion coefficients Aa between the sensor a cap and the host structure Aa = (a cap - astruct). The component of variation of mechanical deformation of the host structure: is then defined by the following equation:

[0191] [Math 35]

[0192] Step E16 concerns the calculation of certain local values ​​of variations in radial displacements Au and longitudinal displacements Aw, of total radial and longitudinal deformations (mechanical + thermal), and of radial stresses Ao rr , by continuity on its common external interface with the host structure.

[0193] It should be noted that the thermomechanical properties (coefficients E, v, a) and the measurement sensitivities (K £ , K P and K T ) correspond to those of the transducer 7 integral with the sensor 3 for the measurement technique considered. If the test body 9 is the micro-structured fiber (microcapillary sealed tightly at its ends), the sensor 3 is then formed of this sealed capillary and its transducers 7. This sensor 3 can then be integrated, in a solid and slightly intrusive manner, within or on the surface of any host structure 19 to measure the local variations in temperature, mechanical deformation (component according to the orientation k of the sensor) and hydrostatic pressure, external to the sensor (corresponding to the variation in the hydrostatic pressure internal to the structure, at the position of the sensor).

[0194] Step E17 concerns selective measurements in the presence of birefringence, and therefore with a separation of the Bragg peak into two distinct wavelengths λ2 and λ3, along a first propagation axis (called ordinary axis or slow axis) and a second propagation axis (called extraordinary axis or fast axis).

[0195] This step illustrates the effect of birefringence on a Bragg grating carried by an optical fiber. The diagram shows the reflection intensity l(X) as a function of the wavelength X before and after the action of a variation in hydrostatic pressure acting on the sensor. Indeed, still depending on the configuration of a sensor 3 integrable in the heart of a structure 19 of any geometry, the hydrostatic pressure acting on the micro-structured optical fiber 9 naturally generates a gradient of deformations in its wall, therefore birefringence. This results in a separation of the original Bragg peak Xi into two distinct Bragg wavelengths λ2 and λ3 along the ordinary and extraordinary axes respectively.

[0196] The hydrostatic pressure exerts, in a way, for this geometry of test body, a "pinching" effect on the Bragg grating, with the consequence of generating or exacerbating a local birefringence (if the optical waveguide is originally strongly birefringent) whose cause is the appearance of a gradient of deformations in the wall of the test body when the latter is subjected to a hydrostatic stress. The positioning angles of the optical fiber 9, in such a case, can be adapted for selective measurements of the mechanical contributions to the deformation of the test body, such as variations in hydrostatic pressure AP or longitudinal forces 6F, other than those exerted by a hydrostatic pressure.

[0197] In this case, for a selective measurement of the variation of the hydrostatic pressure applying to the inside APint or to the outside AP ex t of sensor 3, an angle equal, in absolute value, to the absolute value of the angle 4MP modulo n, is defined for each of the wavelengths À2 and

[0198] X3, according to the following relationships.

[0199] For the wavelength λ2 relative to the ordinary axis, the angle 4JAP is defined by:

[0200] [Math 36]

[0201] 1 2K £

[0202] WAP[ n t <PAP ex t = (o &P = + -arccos —1 + modrr

[0203] " " 2 1 + vJ

[0204] For the wavelength λ3 relative to the extraordinary axis, the 4MP angle is defined by:

[0205] [Math 37] modrr

[0206] On the other hand, for a selective measurement of the variation of longitudinal forces 6F

[0207] (other than exerted by hydrostatic pressure) exerted on the sensor 3, each of the angles

[0208] 'PSFAD int ET 'PSF &APD ext is defined, for each of the wavelengths À2 and À3, according to the following relations.

[0209] For wavelength λ2, the angles (Ps F , o (r i ') and (Ps F , o (r i ') int &P ext with i=l,2, are expressed as follows: [Math 38]

[0210] 1

[0211] (p3F & a P r i. modrr nt (El) = ± - £ arccos

[0212] [Math 39] modrr

[0213] For wavelength λ3, the angles as follows:

[0214] [Math 40]

[0215] 1

[0216] <P3F & a P r i.nt (n) = ± - modrr £ arccos

[0217] [Math 41] modrr

[0218] These effects may however not be significant enough to lead to a clear separation of its spectral profile under the effect of this deformation gradient.

[0219] Fig. 6 is a flowchart illustrating the steps of a non-intrusive method for measuring a longitudinal mechanical deformation (according to the orientation k of the sensor) and / or a variation in hydrostatic pressure relating to a cylindrical structure, of circular section, according to another particular embodiment of the invention.

[0220] This embodiment concerns the case of a sensor according to Figs. 1 to 3B in its version with waveguides (and therefore transducers) integrable in a host structure of cylindrical geometry, of circular section, hollow and sealed at its ends and deforming in its elastic domain. Here, the host structure itself plays the role of the test body.

[0221] Step E21 concerns the configuration of the sensor 3 formed by optical waveguides 7 within the cylindrical host structure.

[0222] At least two optical waveguides 7 (carrying transducers), the mechanical component of the measurement of which is orientation-sensitive, are positioned in the wall of the cylindrical section and / or on one of the surfaces of the host structure 19, but not on its ends, acting as watertight closures (the watertight closure at the ends being to be considered in the broad sense in the sense that it is not necessarily carried out directly on the structure: this concerns for example a pipe used for the extraction of hydrocarbons from the seabed, where the watertight closure can be considered by the well itself on the seabed side for the first end, and by the surface storage station at the other end). The transducers carried by the optical waveguides 7 are configured to measure the mechanical component of the total deformation (resulting from the sum of a mechanical deformation and a thermal deformation).For example, the transducers are Bragg gratings within a single-mode optical fiber in the case of distributed measurements, or simply an optical fiber, preferably single-mode, if it is used in distributed measurement by Brillouin reflectometry, Rayleigh, phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing), etc. The optical fiber may advantageously be provided with an elastically deformable protective sheath, for example made of polymer (polyimide, polyacrylate, etc.). Advantageously, the protective sheath is made of ceramic (eq: boron nitride BN) or metal (eq: copper, aluminum, gold), to support 3D printing implementation processes whose temperatures are likely to be high, in particular in the field of metal 3D and ceramic 3D printing.

[0223] The two transducers carried by the waveguides 7 are locally oriented respectively according to a circular helix with the axis of the cylindrical host structure, of circular section (acting as a test body). The orientation is defined by the same predetermined family of angles 4MP OR relative to a plane normal to the axis of the structure, so as to be able to select, exclusively, one or the other mechanical effect (hydrostatic pressure or longitudinal force, other than exerted by hydrostatic pressure). The two transducers are positioned at two distinct radii ri and r2 or on the internal surface of the radius or external to the radius r Oext , so as to benefit from distinct sensitivities in mechanical deformations, while remaining subject to the same temperature variation. This makes it possible to overcome the effects of temperature variations, and by extension, any other non-mechanical effect such as, for example, those of ionizing radiation on the transducers, by simply subtracting the true relative values ​​from their raw measurements.

[0224] It should be noted that conventional transducers can be used, provided that the mechanical component of the deformation measurement they allow to be carried out is sensitive to the orientation of the transducer relative to the structure acting as the test body. Thus, concerning Bragg gratings, the use of conventional single-mode optical fibers, whose optical guide is on their axis, is perfectly conceivable, with a process of photoinscription of the Bragg gratings which can also be conventional (of the phase mask type or Lloyd mirrors for example), or point-by-point with a femtosecond laser (eq: type III Bragg gratings).

[0225] Depending on the temperature ranges envisaged, the optical fiber can be made in the traditional way from doped silica (case of germanosilicate type optical fibers), or from AI2O3 sapphire, in order to withstand the most extreme temperatures, up to 1000°C continuously, and even beyond (1800°C being an upper limit temperature for sapphire).

[0226] The sensor can be considered as an end component (case of Bragg grating type transducers), or as a distributed measurement sensor (several components coupled in a daisy chain within the same optical fiber), or even a distributed measurement sensor, sensitive over its entire length, for example usable by Brillouin reflectometry,

[0227] OFDR Rayleigh, phase-OTDR (c|)-OTDR) or DAS (Dynamic Acoustic Sensing).

[0228] This sensor 3, formed by the structure 19 playing the role of the test body 9 with the transducers 7 positioned in its wall, makes it possible to carry out a selective measurement of the variations in hydrostatic pressures or longitudinal forces (other than those exerted by hydrostatic pressure).

[0229] Step E22 concerns the selective measurement of the variation in hydrostatic pressure

[0230] APjnt prevailing inside the host structure 19 and the determination of the variation of the local temperature AT associated with the variation of the internal hydrostatic pressure.

[0231] The angles cfi and "t"? are equal, in absolute value, to the absolute value of the angle <p&p int modulo n, the value of which depends on the radial position, on the surface - internal or external - or within the wall of the structure acting as the test body.

[0232] In the case where the transducer is positioned on the internal surface of the radius or external to the radius r Oext of the cylindrical structure, of circular section (Le.: test body), the angle <p&p int is defined by the following relation:

[0233] [Math 42]

[0234] However, in the case where the transducer is positioned in the wall of the cylindrical structure, of circular section (Le.: test body), the angle <PAp mt is defined by the following relation:

[0235] [Math 43] modrr where E is the Young's modulus of the structure, K P and K £ are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the transducer, for the measurement technique considered (for example Bragg grating type), and v is the Poisson's ratio of the structure playing the role of test body.

[0236] The variation of the internal hydrostatic pressure APint is a linear function f^p int of the difference of true relative variations: AT a — AT^ of primary measures: The variation of the hydrostatic pressure APint prevailing inside the structure is given by the following relation:

[0237] [Math 44]

[0238] Explicitly, the variation of the internal hydrostatic pressure APint and the variation of the local temperature AT associated with this variation of the internal hydrostatic pressure are expressed as follows: when the transducers are positioned in the wall of the test body at radii ri and r2:

[0239] [Math 45] where K T is the temperature sensitivity of the transducer, attached to the host structure, for the measurement technique considered (for example Bragg grating type). when the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0240] [Math 47]

[0241] [Math 48] when the transducers are positioned in the wall at radius ri and on the external surface at radius r Oext of the test body:

[0242] [Math 49]

[0243] [Math 50] when the transducers are positioned on the internal surface of the radius and in the wall at radius r2 of the test body:

[0244] [Math 51] when the transducers are positioned on the internal surface of the radius and in the wall at radius r2 of the test body:

[0245] [Math 52]

[0246] Step E23 concerns the measurement of the variation in longitudinal forces 6F (other than those exerted by hydrostatic pressure) exerted on the structure acting as the test body and the variation in the associated local temperature AT.

[0247] The angle cfi ('-e. : <t>i or cfz) is in absolute value, equal to the absolute value of the angle

[0248] <P3F & has P . rint (n) modulo n: [Math 53]

[0249] In the case where the transducer is positioned on the internal surface of the cylindrical structure, of circular section ( / .e.: test body), the angle < is defined by the following relation:

[0250] [Math 54] modîT

[0251] In the case where the transducer is positioned on the external surface of the cylindrical structure, of circular section: test body), the angle (p8 F .„ (r Q J is defined by the ^ int K ext ' following relationship:

[0252] [Math 55] mod n

[0253] In the case where the transducer is positioned in the wall of the cylindrical structure (Le.: body is defined by the following relationship:

[0254] [Math 56] modrr

[0255] The variation of longitudinal forces 8F &Pint exerted on the test body (Le.: the cylindrical structure of circular section,) is a linear function fsF â^ F, of the difference of the int variations of the true relative values: AT a — A 4^ of primary measures and 'Pb: [Math 57]

[0256] Explicitly, the variation of longitudinal forces 8F^ Pint and the variation of the corresponding local temperature AT are equal to: when the transducers are positioned in the wall of the test body at radii ri and r2:

[0257] [Math 58] [Math 59] when the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0258] [Math 60]

[0259] [Math 61] when the transducers are positioned in the wall at radius ri and on the external surface at radius r Oext of the test body:

[0260] [Math 62]

[0261] [Math 63] when the transducers are positioned on the internal surface of the radius and in the wall at radius r2 of the test body:

[0262] [Math 64]

[0263] [Math 65]

[0264] Steps E24-E25 represent a variant of measuring the variation of hydrostatic pressure, the variation of longitudinal forces (along the axis of the structure) and the variation of local temperature.

[0265] More particularly, in step E24 the sensor 3 is configured to selectively measure the variation in the hydrostatic pressure AP ex t prevailing outside the structure 19. In addition, the calculator determines the variation of the local temperature AT associated with the variation of external hydrostatic pressure.

[0266] In this case, the angles cfi and <t>2 are equal, in absolute value, to the absolute value of the angle <p^p ext modulo n, the value of which depends on the radial position, on the surface - internal or external - or in the wall of the structure acting as the test body.

[0267] In the case where the transducer is positioned on the internal surface of the radius or external to the radius r Oext of the cylindrical structure (Le.: test body), the angle <P&p ext is defined by the following relation:

[0268] [Math 66]

[0269] However, in the case where the transducer is positioned in the wall of the cylindrical structure, of circular section (Le.: test body), the angle <P&p ext is defined by the following relation:

[0270] [Math 67] where E is the Young's modulus of the structure, K P and K £ are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the transducer for the measurement technique considered (for example Bragg grating type), and v is the coefficient of

[0271] Fish of the structure playing the role of the test body. The variation of the external hydrostatic pressure AP ex test a linear function f^p ext of the difference of true relative variations: AV a — AV b primary measures: V a and V b . The variation of hydrostatic pressure AP ex t reigning outside the structure is given by the following relation:

[0272] [Math 68]

[0273] Explicitly, the variation of the external hydrostatic pressure AP ex t and the variation of the associated local temperature AT are expressed as follows: when the transducers are positioned in the wall of the test body at radii ri and r2:

[0274] [Math 69] when the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0275] [Math 71]

[0276] [Math 72] when the transducers are positioned in the wall at radius ri and on the external surface at radius r Oext of the test body:

[0277] [Math 73]

[0278] [Math 74] when the transducers are positioned on the internal surface of the radius and in the wall at radius r2 of the test body:

[0279] [Math 75]

[0280] [Math 76]

[0281] Step E25 concerns the measurement of the variation in longitudinal forces 6F (other than those exerted by hydrostatic pressure) exerted on the structure acting as the test body. In addition, the calculator determines the variation in local temperature AT associated with this variation in longitudinal forces 6F.

[0282] The angle cfi ('-e. : <t>i or cfz) is in absolute value, equal to the absolute value of the angle 1, 2

[0283] In the case where the transducer is positioned on the internal surface of the cylindrical structure, of circular section (Le.: test body), the angle (p$ F .„ (r0. A is defined by the following relation:

[0284] [Math 78] In the case where the transducer is positioned on the external surface of the cylindrical structure, of circular section (i.e.: test body), the angle (p$ F .„ (r0 / ) is defined by the following relation:

[0285] [Math 79] modrr

[0286] In the case where the transducer is positioned in the wall of the cylindrical structure

[0287] (ie: circular section test body is defined by the following relation:

[0288] [Math 80] modrr

[0289] Measurement of the variation of longitudinal forces 8F^ Pext exerted on the test body (ie: the cylindrical structure of circular section) is a linear function fsp. D of ^ P ext the difference of true relative variations: AT a — AT^ of primary measures: And :

[0290] [Math 81]

[0291] Explicitly, the variation of longitudinal forces 8Fs FriD and the variation of the associated local temperature AT, are given by: when the transducers are positioned in the wall of the test body at radii ri and r2:

[0292] [Math 82]

[0293] [Math 83] when the transducers are positioned on surfaces internal to the radius r0 and external to the radius r Oext of the test body:

[0294] [Math 84] [Math 85] when the transducers are positioned in the wall at radius ri and on the external surface at radius r Ot.ït of the test body:

[0295] [Math 86]

[0296] [Math 87] when the transducers are positioned on the internal surface of the radius and in the wall at radius r2 of the test body:

[0297] [Math 88]

[0298] [Math 89]

[0299] It should be noted that the measurements according to steps E22-E25 (whether for the variation of the internal or external hydrostatic pressure, or the variation of the longitudinal forces or the variation of the local temperature) can be applied to all configurations of radial position of the transducers, in particular when at least one of them is positioned on the internal or external surface of the test body. Step E26 concerns the calculation of the variation of longitudinal mechanical deformation of the test body The variation of longitudinal mechanical deformation of the body Ae test meCcap is defined by the following equation: [Math 90]

[0300] According to this configuration, the host structure 19 plays the role of the test body 9 and consequently, the component of the variation of longitudinal mechanical deformation A£ m ec struct of the host structure is equal to the variation of longitudinal mechanical deformation of the test body Ae meCcap .

[0301] Step E27 concerns the calculation of the values ​​of the displacements and the components of the strain and stress tensors.

[0302] On the other hand, according to this configuration where it is the structure itself which plays the role of test body and standard single-mode optical fibers, provided for example with a polymer sheath, are used for the measurement, the birefringence effect created by the structure within the optical fiber can remain negligible, and consequently not be taken into account when exploiting the measurement (except in the case of using optical fibers which are already highly birefringent, in which case, the birefringence of these optical fibers will then be exacerbated by the mechanical effects induced by the host structure).

[0303] It will be noted that the methods relating to Figs. 5 and 6 also apply to the embodiment of Figs. 3A and 3B in which the sensor 3 is advantageously formed from two pairs of transducers. These transducers are oriented locally according to the angles distinct radii r, „ „ , r-, . This allows to measure simultaneously, y SF toP ext 2 sF M>ext according to an intrinsic selectivity, the two mechanical effects of variation of external hydrostatic pressure AP ex test of variation of longitudinal mechanical forces 6F applied to the test body (distinct from those exerted by hydrostatic pressure), as well as the associated variations AT of the local temperature.

[0304] Advantageously, the methods described above provide complete calculation formulas corresponding to the vast majority of possible variations in terms of combinations of radial positions and orientations of the transducers, as long as the calculations are possible (in particular concerning the remarkable angles, which must necessarily take a real value).

[0305] Fig. 7A illustrates a sensor for selectively measuring the variation in hydrostatic pressure AP applied to the sensor, according to a third embodiment of the invention.

[0306] The sensor 3 according to this third embodiment comprises a single optical waveguide 7 oriented locally in a circular helix around the axis of revolution of the test body 9 at the angle 4JAP relative to a plane normal to the axis of revolution of the test body. The optical waveguide 7 is positioned at a radius r in the elastic wall of the test body 9. According to this example, the optical waveguide is intrinsically a transducer corresponding to an optical fiber, preferably single-mode, using a continuously sensitive distributed measurement reflectometric technique, of the Brillouin type, based on the Landau-Placzek ratio to carry out an intrinsic measurement of the variation in hydrostatic pressure. The temperature information is generally additional information provided directly by the measurement technique in question (see document EP 3 232 165).

[0307] In such a case, the variation: of the internal hydrostatic pressure APint in the test body is given by: [Math 91] of external hydrostatic pressure AP ex t to the test body is given by:

[0308] [Math 92] where ÛEmec is the variation of mechanical deformation of the structure, according to the orientation of the optical fiber, carried out by the measurement technique in question between the current state and the reference state of the structure, and K P and K £ are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the measurement technique considered for the waveguide in question.

[0309] Fig. 7B is a variant of the third embodiment according to which the sensor 3 is intended to selectively measure the variation of the longitudinal force 6F (other than exerted by hydrostatic pressure) applied to the test body.

[0310] According to this variant, the single optical waveguide 7 is locally oriented in a circular helix around the axis of revolution of the test body 9 according to the angle with respect to a plane normal to the axis of revolution of the test body. The optical waveguide 7 is positioned at a radius r in the elastic wall of the test body 9. Here too, a continuously sensitive distributed measurement reflectometric technique, of the Brillouin type, is used, based on the Landau-Placzek ratio to achieve an intrinsic separation of the longitudinal mechanical deformation and the temperature.

[0311] In such a case, the variation of the longitudinal force 6F: independently of the variation of the internal hydrostatic pressure APint applied to the test body, is given by:

[0312] [Math 93] regardless of the variation of the external hydrostatic pressure AP ex t applied to the test body, is given by:

[0313] [Math 94] where AEmec is the variation in mechanical deformation of the test body structure, depending on the orientation of the waveguide, achieved by the measurement technique in question between the current state and the reference state of the structure, and K P and K £ are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the measurement technique considered for the waveguide in question.

[0314] Fig. 8A illustrates a sensor intended to selectively measure, with or without exploitation of birefringence, the variation of the hydrostatic pressure AP and the variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body, according to a fourth embodiment of the invention.

[0315] The sensor 3, according to this fourth embodiment, comprises first 7a, second 7b and third 7c optical waveguides oriented locally in a circular helix around the axis of revolution of the test body 9. The three waveguides 7a, 7b, 7c are positioned in the elastic wall of the test body at any angles, but at least two of them are, in absolute value, distinct modulo n: cf(ri), <t>(r2) and ^(ra), and according to the radii: ri, fi and ra, at least two of which are distinct. Each of the three waveguides carries a Bragg grating type transducer 11a, 11b, 11c. The three transducers 11a, 11b, 11c are preferably positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature.

[0316] Thus, this sensor 3 makes it possible to selectively measure the variations in hydrostatic pressure AP (internal and / or external) and longitudinal force 6F (other than exerted by hydrostatic pressure), as well as the variation in temperature AT, thanks to the use of the formal solution of the underlying thermomechanical problem.

[0317] These solutions are given, for transducers positioned in the thickness of the test body (which represents the majority of application cases), by the following expressions: when the formal problem is solved according to the 3 unknowns { APint, 6F, AT}: concerning the variation of the internal pressure APint:

[0318] [Math 95] regarding the temperature variation AT:

[0319] [Math 96]

[0320] when the formal problem is solved according to the 3 unknowns { AP ex t, 5F, AT}: concerning the variation of external pressure AP ex t:

[0321] [Math 97]

[0322] - regarding the temperature variation AT:

[0323] [Math 98]

[0324] The formula leading to the variation of the longitudinal force 6F is identical according to the two modes of resolution of the formal problem:

[0325] [Math 99]

[0326] It should be noted that the procedure described in Fig. 4 allows, among other things, to obtain a measurement of the variation of the longitudinal mechanical deformation of the test body A£ meCcap and the variation of the mechanical deformation Mue Ae m m p e r c struct of the host structure depending on the orientation of the sensor, applies in the same way.

[0327] Fig. 8B is a variant of the fourth embodiment also for selectively measuring, with or without exploitation of birefringence, the variations of the hydrostatic pressure AP and the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body. According to this variant, the three waveguides 7a, 7b, 7c are exploited by a distributed measurement reflectometric technique on optical fiber, sensitive both to temperature and to mechanical deformation, such as the Brillouin, OFDR Rayleigh, phase-OTDR (c|)-OTDR) and DAS (Dynamic Acoustic Sensing) techniques.

[0328] Thus, the sensor 3, according to the different embodiments of the present invention, makes it possible to separate the effects of temperature, hydrostatic pressure and longitudinal mechanical deformation, in order to provide independently of one another, since the transducers implemented within the sensor are sensitive to these three effects, the local measurement of the variations of each of these three effects with respect to an arbitrary reference state. This is valid whether in the case of a micro-structured fiber or in the case of a structure acting as a test body itself acting as a sensor (e.g.: tank or pressurized pipe).

[0329] The provision of formal expressions in hydrostatic pressure variation and longitudinal mechanical deformation variation according to a given orientation (the (zz) axis of the sensor) is a real added value, in the sense that they can allow the experimenter to do without calibration for his measurement, as long as the thermomechanical properties of the test body, in the temperature ranges considered, and its reference state, are known with sufficient precision.

[0330] None of the state-of-the-art non-intrusive (or weakly intrusive) solutions allows the separation of the two mechanical effects (pressure and longitudinal force) from non-mechanical effects such as temperature and / or the effects of ionizing radiation, independently of each other, whether or not the sensor is embedded in a deformable structure.

[0331] Furthermore, it is possible to simultaneously provide information on the variation of hydrostatic pressure and the variation of longitudinal mechanical deformation according to a given orientation thanks to the combination of two separate sensors, each based on its family of angles for intrinsic selectivity of the measurements, in which case 2x2=4 transducers are used if the measurement technique implemented does not allow the mechanical effects to be intrinsically separated from non-mechanical effects (such as temperature and / or the effects of ionizing radiation).

[0332] It should be noted that it is also possible to use only three transducers if the families of remarkable angles, allowing the selectivity of one or the other mechanical effect (hydrostatic pressure or longitudinal force), are not used, in which case the solution allowing their formal expression is of greater complexity as shown by the expressions in the absence of birefringence cited above in this document, and consequently more subject to measurement uncertainties. The use of three transducers nevertheless has the major advantage of always having a real solution, the angles being able to be arbitrary, at least two of them having to be, in absolute value, distinct modulo n, facilitating the implementation of the sensor on the one hand, and allowing the use of radii of curvature of the waveguides sufficiently large not to lead to excessive optical losses on the other hand.

[0333] And although this is not its main characteristic, the sensor, in each of its variants, makes it possible to provide additional information on local temperature variation since the measurement technique implemented, for the transducers considered, is itself sensitive to temperature, since temperature is the only non-mechanical phenomenon to which the transducers are subjected.

[0334] The sensor can be used for the instrumentation of Type IV composite tanks for the high-pressure storage of gaseous molecular hydrogen H2, so as to be able to monitor their health status throughout their operation. This is particularly advantageous during the filling phases where the tank is subjected to both strong temperature variations (temperature rise up to +70°C), as well as strong variations in stress (700 bar at operating pressure) and deformation (0.6% in elongation at operating pressure, and up to 2% at the tank's breaking limit), where consequently the risk of bursting is highest.

[0335] The simultaneous use of a pressure measurement in contact with the fluid within the tank then makes it possible to construct a tank damage parameter which can be used to detect the moment from which it must be scrapped due to a high risk of bursting.

[0336] Such a sensor, in a configuration with Bragg grating transducers, would thus make it possible to provide the health status of the tank in real time, unlike a Rayleigh OFDR type measurement technique which remains sensitive to vibrations, and moreover to the effects of temperature (see L. Maurin et al. "OFDR Distributed Strain Measurements for SHM of Hydrostatic Stressed Structures: An Application to High Pressure Hydrogen Storage Type IV Composite Vessels - H2E Project". <hal-01021252>).

[0337] More generally, the sensor can be used for instrumentation at the heart of any deformable structure for its in situ monitoring, during its use, in particular composite structures, since the optical fiber fits perfectly without generating additional defects which could lead to local weakening.

[0338] Other types of structures (metallic, ceramic, polymer, composite) can be considered as long as the sensor can be inserted into them, for example when these structures are manufactured by additive manufacturing. Surface instrumentation is also perfectly feasible.

[0339] The host structure can be made of composite material (the preferred material for optical fibers, which are inserted fairly easily without generating any additional structural defects, provided that the fibers are oriented in the same direction as the reinforcing fibers). This is the typical case for type IV tanks for high-pressure storage of molecular hydrogen H2 gas. The host structure can be made of any other material, for example metal, plastic, or ceramic (the structure can be composite, i.e. made of materials of various types), and the sensor can then be inserted into the part to be instrumented during its manufacture.

[0340] The present invention has industrial applications in any sector where the measurement of directional mechanical deformations, as well as the measurement of hydrostatic pressures within a deformable mechanical structure, are of interest. In particular, to carry out measurements during the manufacturing process of an instrumented part, for example to validate calculation codes, or even to improve the manufacturing process in question, thanks to in situ measurements, and once the part is manufactured, the invention makes it possible to ensure its health control throughout its lifetime.

[0341] Any installation comprising a pressurized structure can be instrumented. Thus, the invention is also suitable for pressurized pipes as long as it is possible to insert the sensor (in its micro-structured fiber version) or to insert optical measurement fibers (case of pipes made of composite materials, such as the hoses used for transporting hydrocarbons from the seabed) in the case where it is the pipe itself which acts as the test body. It should be remembered that a pipe can, during its use, generally be considered as being sealed at its ends. < / t> < / t> < / t> < / t> < / pm> < / t> < / t>

Claims

CLAIMS 1. Non-intrusive measuring device intended to measure a variation in longitudinal force, other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relative to a host structure of interest, comprising: - a sensor (3) comprising at least one optical waveguide (7) installed integrally on one of the surfaces or in the wall of a cylindrical test body (9), of circular section, hollow and sealed at its ends, deforming in its elastic domain, each optical waveguide locally describing a circular helix positioned at a radius r around the axis of revolution of the test body (9) and oriented locally according to a predetermined angle <t»(r) par rapport à un plan normal au dit axe de révolution, chaque guide d'onde (7) portant au moins un transducteur (11) dont la composante mécanique de la mesure est sensible à l'orientation et configuré pour réaliser une mesure sélective d'une première variable primaire, dont la variation relative vraie par rapport à un état de référence est représentative d'une variation locale de pression hydrostatique appliquée au corps d'épreuve (9) ou d'une deuxième variable primaire,whose true relative variation with respect to a reference state is representative of a local variation of longitudinal force, other than exerted by hydrostatic pressure, applied to the test body, the selectivity of one or the other mechanical effect by means of the first and second primary variables being ensured by the orientation of each waveguide, and, - a calculator (17) configured to selectively calculate the local variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body and / or the local variation of the hydrostatic pressure AP applied to the test body (9) as a function of the true relative variations of the measurements of said first and / or second primary variables.

2. Device according to claim 1, characterized in that the calculator (17) is further configured to calculate the variation of the local temperature as a function of the true relative variations of the measurements of said first and / or second primary variables.

3. Device according to claim 1 or 2, characterized in that the calculator (17) is configured to calculate the local variation of the longitudinal mechanical deformation Ae mec; ^ of the test body (9) as a function of the local variation of the longitudinal force 6F, other than exerted by a hydrostatic pressure, and the local variation of the hydrostatic pressure AP applied to the test body, as well as the physical parameters of the test body (9).

4. Device according to any one of the preceding claims, characterized in that it comprises at least one pair of optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body (9) and carrying at least one pair of transducers (11a, 11b), the optical waveguides forming each pair being positioned according to two distinct radii ri and r2 around the axis of revolution of the test body (9) and oriented locally according to a pair of predetermined angles relative to a plane normal to said axis of revolution.

5. Device according to any one of the preceding claims, characterized in that it comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body according to first and second angles distinct with respect to a plane normal to the axis of revolution, the first optical waveguide being dedicated to measuring the variation in hydrostatic pressure AP, the second optical waveguide being dedicated to measuring the variation in longitudinal force 6F, other than exerted by hydrostatic pressure, applied to the test body.

6. Device according to any one of claims 1 to 4, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body according to the same family of angles {(pSF^s^. ipSF^sF)) with respect to a plane normal to the axis of revolution, the first family of angles being dedicated to the selective measurement of the variation in hydrostatic pressure AP, while the second family of angles is dedicated to the selective measurement of the variation in the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body.

7. Device according to claim 6, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body, according to first and second angles P ar relative to a plane normal to the axis of revolution of the test body, these angles taking a first identical and constant value in the wall of the test body and a second identical and constant value on the internal and external surfaces of the test body, the first and second angle values ​​being distinct, said first and second optical waveguides being dedicated to the selective measurement of the variation in hydrostatic pressure AP.

8. Device according to claim 6, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body, according to first and second angles <p5 distinct with respect to a plane normal to the axis of revolution of the test body, said first and second optical waveguides being dedicated to measuring the variation of the longitudinal force 6F, other than exerted by hydrostatic pressure, applied to the test body.

9. Device according to any one of claims 1 to 4, characterized in that it comprises first and second pairs of optical waveguides (7a, 7b, 7c, 7d) positioned locally in a circular helix around the axis of revolution of the test body (9) according to distinct radii r lâp , r 2&p , r lg , and r 2gF , the two waveguides of the first pair are positioned at first and second angles P ar relative to a plane normal to the axis of revolution of the test body, these angles taking a first identical and constant value in the wall of the test body and a second identical and constant value on the internal and external surfaces of the test body, the first and second angle values ​​being distinct, while the two waveguides of the second pair are positioned according to two distinct angles P arrelative to a plane normal to the axis of revolution, the first pair of waveguides being dedicated to measuring the variation in hydrostatic pressure AP, while the second pair of waveguides is dedicated to measuring the variation in longitudinal force 6F, other than exerted by hydrostatic pressure, applied to the test body.

10. Device according to any one of claims 1 to 3, characterized in that it comprises a single optical waveguide (7) positioned at a predetermined radius in the elastic wall of the test body and oriented locally in a circular helix around the axis of revolution of the test body (9) at a predetermined angle relative to a plane normal to the axis of revolution, the optical waveguide being dedicated to measuring the variation in hydrostatic pressure AP or to measuring the variation in the longitudinal force 6F, other than exerted by hydrostatic pressure, applied to the test body, using a continuously sensitive distributed measurement technique of the Brillouin reflectometry type, based on the Landau-Placzek ratio.

11. Device according to any one of claims 1 to 3, characterized in that it comprises first, second and third optical waveguides (7a, 7b, 7c) oriented locally in a circular helix around the axis of revolution of the test body (9) according to first, second and third radii ri, r2 and r3, at least two of which are distinct and according to first, second and third angles, cf(ri), ^(rj) and ^(ra) relative to a plane normal to the axis of revolution, at least two of which are, in absolute value, distinct modulo n, the first, second and third optical waveguides being dedicated to the measurement of the variation in hydrostatic pressure AP and the variation in the longitudinal force 6F, other than exerted by a hydrostatic pressure, applied to the test body, as well as the local variation in temperature AT since no other non-mechanical effect other than that of the temperature does not act on the transducers,and that the raw measurement made by each transducer is itself sensitive to temperature.

12. Device according to any one of the preceding claims, characterized in that each optical waveguide (7) carries a transducer (11) according to a Bragg grating type technique suitable for carrying out distributed measurements.

13. Device according to any one of claims 1 to 10, characterized in that each optical waveguide (7) carries a transducer according to a continuous technique of the Brillouin reflectometry, OFDR Rayleigh, phase-OTDR or DAS type, adapted to carry out measurements distributed along the optical waveguide.

14. Device according to any one of claims 1 to 5, 7 to 10, 12 and 13, characterized in that the sensor (3) comprises said cylindrical test body (9) of circular section and delimiting a sealed cavity, and in that it is intended to be installed in any host structure (19), the variation in external hydrostatic pressure AP ex t and the temperature variation ATi associated with the hydrostatic pressure, as well as the variation of the longitudinal force SF &Pext , other than exerted by hydrostatic pressure, and the temperature variation AT2 associated with the calculation of the longitudinal force being defined according to the following equations, since the test body deforms in its elastic domain: [Math 1] where AT is the true relative variation of the raw value T corresponding to the primary measurement made by the transducer between its reference value T oand its current value T, E is the Young's modulus of the test body, v is the Poisson's ratio of the test body, K P , K £ and K T are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation and in temperature of the transducer integral with the host structure for the measurement technique considered (for example Bragg grating type), APint is the variation of the internal hydrostatic pressure, r0, r Oext are respectively the internal and external radii of the optical fiber in its reference state, and r 1; r2 are respectively the radii corresponding to the positioning of the first and second transducers.

15. Device according to claim 14, characterized in that the test body (9) is a micro-structured optical fiber forming a micro-capillary sealed at its ends.

16. Device according to claim 14 or 15, characterized in that the test body (9) is coated with a deformable mechanical sheath of polymer type.

17. Device according to any one of the preceding claims, characterized in that the sensor (3) is configured to exploit a birefringence effect within the optical waveguide.

18. Device according to any one of claims 1 to 5, 7 to 10, and 12 to 17, characterized in that the host structure has a cylindrical shape, of circular, hollow and closed section of sealed manner at its ends, then playing the role of test body (9), the variations in internal hydrostatic pressures APint and external AP ex t, the variations of the associated longitudinal forces 8F &Pint and 8F &Pext, other than exerted by hydrostatic pressure, and the associated temperature variations ATi, AT2, AT3, AT4 being defined according to the following equations, as soon as the structure deforms in its elastic domain, with transducers positioned in the wall of the structure, at radii ri and r2: [Math 3] where AT is the true relative variation of the raw value T (i.e.: primary measurement made by the transducer) between its reference value T o and its current value T, E is the Young's modulus of the structure, v is the Poisson's ratio of the structure, K P , K £ and K T are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation and in temperature of the transducer attached to the host structure for the measurement technique considered (for example Bragg grating type), and r0 , r Oextare respectively the internal and external radii of the cylindrical structure in its reference state, and r 1; r2 are respectively the radii corresponding to the positioning of the first and second transducers.

19. Device according to any one of claims 1 to 12, characterized in that the structure (19) has any shape and in that the cylindrical test body (9) of circular section is housed in the structure.

20. Installation characterized in that it comprises: - a structure whose hydrostatic pressure and / or longitudinal mechanical deformation and / or temperature are to be monitored, and - a measuring device (1) according to any one of claims 1 to 16.

21. Non-intrusive method for measuring a variation in longitudinal force and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising the following steps: - positioning at least one optical waveguide (7) locally describing a circular helix on one of the surfaces or in the wall of a cylindrical test body (9), of circular section, hollow and sealed at its ends, each optical waveguide being positioned at a radius r around the axis of revolution of the test body and being oriented locally according to a predetermined angle <t»(r) par rapport à un plan normal au dit axe de révolution, chaque guide d'onde portant moins transducteur (11) dont la composante mécanique mesure primaire est sensible l'orientation,- carrying out by means of at least said transducer (11) a selective measurement of a first primary variable, the true relative variation of which with respect to a reference state is representative of a local variation of hydrostatic pressure applied to the test body or of a second primary variable, the true relative variation of which with respect to a reference state is representative of a local variation of longitudinal force, other than exerted by a hydrostatic pressure, applied to the test body, the selectivity of one or other of the first and second primary variables being ensured by the orientation of each waveguide, and - selectively calculating the local variation of the longitudinal mechanical deformation of the test body and / or the local variation of hydrostatic pressure applied to the test body as a function of the true relative variations of the measurements of said first and / or second primary variables.

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